Al/Ce/Zr oxide composites with incorporated catalytically active noble metals are known and are used for catalytic exhaust gas aftertreatment, for example, of combustion gases in particular, which have been discharged from the combustion chamber(s) of motor vehicles. Such automotive catalysts usually consist of multiple components. A thermally stable honeycomb body made of ceramic, usually cordierite, or metal films having a plurality of thin-walled channels is used as the carrier. The so-called wash coat, comprising porous aluminum oxide (Al2O3) and oxygen storage components, is applied to the carrier. The wash coat also contains catalytically active noble metals incorporated into it. In modern exhaust gas catalysts, these are platinum, rhodium and/or palladium. The ceramic carrier is supported in a metallic housing with the help of special bearing mats made of high-temperature wool, for example, less often in combination with wire mesh. Wash coats containing Al/Ce/Zr oxide composites are known for aftertreatment of exhaust gas of combustion engines in which the cerium/zirconium mixed oxides act as oxygen storage components. The Al/Ce/Zr oxide composites according to this invention are used in the above automotive catalysts.
WO 2006/070201 A2 describes an improved variant for producing mixed oxides of aluminum oxide, zirconium oxide and optionally at least one representative from CeO2, La2O3, Nd2O3, Pr6O11, Sm2O3, Y2O3 and possibly other rare earth oxides. Production is based on joint precipitation of the corresponding salts. The mixed oxides are produced by joint precipitation of all the oxides involved, starting from a metal salt solution, where the pH is adjusted in the range of 8.5±1 during precipitation. Precipitation is performed by adding alkali hydroxides, in particular sodium hydroxide solution.
WO 2008/113457 A1 describes the production of Al/Ce/Zr oxide composites based on mixtures of aluminum oxide and cerium/zirconium mixed oxides that are produced separately.
U.S. Pat. No. 5,883,037 describes the importance of the thermal stability of the composite materials. The process described here is a multistep process, in which Ce, Zr and optionally Pr salts are first precipitated by raising the pH and then the precipitate is isolated. The precipitate is brought into contact with alumina while mixing, then isolated and subjected to drying and calcination. The alumina is preferably stabilized by foreign ions from the group of rare earths, Ba, Zr or Si. The Ce/Zr mixed oxides and Ce/Zr/Pr mixed oxides produced by precipitation may optionally also be stabilized, e.g., by at least one element of group VIII, bismuth or some other rare earth element. One disadvantage of this production process is due to the low homogeneity of the resulting material.
EP 1172139 A1 describes the production of homogeneous Al2O3/CeO2/ZrO2/Y2O3/La2O3 mixed oxides by coprecipitation as well as their thermal stabilities. In the process described there, the Al—Ce—Zr—Y—La hydroxide intermediates resulting from joint precipitation were calcined and thus converted to the oxides.
WO 2006/119549 A1 describes a process in which a solution of metal salts is added to an acidic boehmite suspension to obtain a second suspension. Precipitation is induced by dropwise addition of the second suspension to an alkaline solution. The method of WO 2006/119549 A1, as also shown by Examples 1 and 2, leads to the development of discrete islands of Ce/Zr/rare earth mixed oxide in addition to aluminum oxide. A very similar process is described in Comparative Examples 3, 14 and 15 of U.S. Pat. No. 6,831,036. The residual surface areas described there are max. 39 m2/g after calcination at 1000° C. for three hours due to the process.
WO 2012/67654 A1 describes a process in which Al/Ce/Zr/rare earth oxide composite is produced by a two-step precipitation. In the first step here an “aluminum hydrate” and optionally a rare earth hydroxide are produced by precipitation of aluminum sulfate with sodium aluminate. After renewed acidification of the suspension, then the Ce/Zr/rare earth component is precipitated by adding the corresponding salt solution to this suspension and then increasing the pH again. The Al/Ce/Zr/rare earth oxide composite thereby obtained should have a surface area (in m2/g) that can be obtained from the formula SA=0.8235·[Al]+11.157 after calcining at 1100° C. for five hours. The residual surface area of the materials after calcining at 1200° C. for five hours is obtained by the formula SA=0.3·[Al]+7. WO 2012/67654 A1 was published subsequently. The respective priority application relates to a different subject matter than that indicated above.